Understanding Technical Terms - Control Valve Vendor sheet

[Iomcube]

There are some terms highlighted in the Flowserve Control Valve sheet that I wasn't able to grasp. Valve is liquid servicing

The inlet pressure is ~13 barg where as Choked Drop is ~0.2 bar ( I do have understanding of choked pressure)

On 2nd page there is a weird term Detailed Cavitation (Sigma) information? What is this & how is it useful?

 

[LittleInch]

Well the service you are looking at is very odd.

I mean you are trying to control a pressure drop of 0.19 bar in 12.6 outlet for two different flows.

This makes no sense to me, but the pressure drop is so small I'm not surprised that the other numbers are very odd.

If you look carefully you can see that the difference between the two flows is 4% of travel.

The detailed sigma stuff I have no idea about, but why on earth this valve exists is simply beyond me.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Iomcube]

LittleInch, the valve is yet to be purchased. If you can give me some pointers at what you feel is weird it will help my judgement because something that comes out of Flowserve is trusted blindly here

 

[LittleInch]

What's weird is what you're asking this valve to do (i.e. virtually nothing). I'm very sure FS have done it correctly, but they've just plugged in the numbers you presumably gave them - it's those numbers which don't look right to me.

If you're serious about having a minute pressure drop but need to control the outlet pressure very precisely, then I can't see 4% of travel from one flow rate tot he next doing it. I think this valve will continuously hunt up and down.

The issue here IHO, is whoever wrote such a data sheet for this valve without considering the practicalities of getting a valve to do the duty.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[jari001]

Can you contact Flowserve to have them explain that portion of the datasheet? If you Google "Detailed Cavitation (Sigma)" you will find some references that discuss lowercase sigma as the cavitation parameter - perhaps your question can be answered there.

 

[Caloooomi]

Look up the Flowserve cavitation control leaflet for information about the sigma values. As jari001 mentions, it is do with predicting cavitaiton

 

[georgeverghese]

Turndown case is missing for this control valve. Check that this dp of 0.2bar is at least 30% of the total frictional drop for this segment.